Background Information: Harmful Algal Blooms
Algae are critical to life on Earth. Because they are able to
convert solar energy into chemical energy through
photosynthesis, algae are key primary producers in many marine
food webs (that is, they provide the primary energy source for
many other marine organisms). Oxygen is another product of
photosynthesis, and single-cell algae (phytoplankton) living in
the ocean are responsible for half of the oxygen produced on
Earth. There are thousands of species of beneficial algae; but there are also a few dozen
species that cause problems. These species become noticeable during periodic events
known as “harmful algal blooms” (HABs). In the last two decades, HABs are estimated to
have caused as much as $1 billion in losses to coastal resources and communities.
The specific events that accompany HABs vary depending upon the species of algae
involved. In some cases, algae grow at unusually rapid rates and overgrow other species,
alter habitats, or deplete oxygen (even though the algae produce oxygen while they are
alive, large amounts of decaying algae can consume enough oxygen to cause a net
depletion). Rapid growth of phytoplankton may produce enough cells to discolor the water.
When discoloration occurs, the event is often called a “red tide,” even though the actual
discoloration may be green, yellow, or brown, as well as red; and the event has nothing to
do with tides. Some algae are capable of producing powerful toxins that are harmful or
deadly to other species. Observed impacts of HABs may include fish kills, injuries to marine
invertebrates, and human illness or death.
The causes of HABs are not fully understood. In some cases, environmental changes such
as alteration in water flow or water temperature have been observed to coincide with HABs.
To live and grow, all plants need certain chemicals known as nutrients. Nitrates and
phosphates are familiar examples. In many aquatic ecosystems, nutrients are scarce and
this limits plant growth. When additional nutrients are added by various types of water
pollution, this control is removed, often resulting in rapid growth of aquatic plants. When
these plants die, the large mass of decaying vegetation depletes oxygen in the water and
damages many other organisms in the system. Scientists suspect that increases in nutrients
may also play a role in some HAB events.
HABs are becoming a global threat to living resources, fishing, tourism, and human health
because the number and intensity of these events appear to be increasing in many
countries. In 1987, the United Nations established a program focussed specifically on HABs
and their impacts. In the United States, a research program on the Ecology and
Oceanography of Harmful Algal Blooms (ECOHAB) was launched in 1995 to develop
methods for predicting where and when HABs are likely to occur, as well as techniques for
preventing and controlling these events. The National Centers for Coastal Ocean Science (an
office of the National Ocean Service) is the primary administrator of ECOHAB, and sponsors
the program in partnership with the National Science Foundation, EPA, NASA, and the Office
of Naval Research.
Resources
http://oceanservice.noaa.gov/hazards/hab/welcome.html